Backlights are used to illuminate liquid crystal displays (LCDs). LCDs with backlights are used in small displays for mobile phones, personal digital assistants (PDAs), portable computers, as well as in large displays for computer monitors and televisions. Often, the light source for the backlight includes one or more cold cathode fluorescent lamps (CCFLs). The light source for the backlight can also be an incandescent light bulb, an electroluminescent panel (ELP), or one or more hot cathode fluorescent lamps (HCFLs).
As costs of light emitting diodes (LEDs) are reduced and their quality is improved, the display industry is enthusiastically pursuing the use of light emitting diodes (LEDs) as the light source in backlight display technology because CCFLs have many shortcomings: For instance, CCFLs do not easily ignite in cold temperatures, they require adequate idle time to ignite, and they require delicate handling. In addition, LEDs have response times substantially faster than CCFLs. Moreover, the color gamut afforded by LEDs is wider than other light sources employed for backlighting and thus provide more vivid color. Furthermore, LEDs generally have a higher ratio of light generated to power consumed than other backlight sources. Accordingly, displays with LED backlights can consume less power than other displays, which renders LED-based displays more sustainable. LED backlighting has traditionally been used in small, inexpensive LCD panels. However, LED backlighting is becoming more common in large displays such as those installed in computers and television sets. In large LCD displays, several LEDs are generally required to provide adequate backlight for the LCD panel; based on specifics of the display, the number of LEDs can reach several hundreds.
Conventional displays such as those based on cathode ray tubes (CRTs) often have a fixed gamma characteristic which determines luminance of such displays. The gamma characteristic and thus the luminance is predetermined in accordance with a standard and generally suited for images that have been prepared for rendition in CRT-based displays. The gamma characteristic establishes a relationship amongst luminance (Ilum) of a display and backlight illumination intensity (IB) and magnitude (VD) of a signal related to data (e.g., an image data) to be displayed in the display. Typically, the relationship is a power relationship defined by a gamma value γ, such that I1um=κ(VD)γIB, where κ is an efficiency coefficient independent of γ. The gamma value γ thus defines the gamma characteristic. In an LCD display with LED-based backlighting, several LEDs utilized for backlighting can be partitioned into regions that span a display area of the LCD display. Brightness of at least one of such regions can change dynamically based on content (e.g., data) of an image to be rendered through pixel circuitry in the LCD display. Thus, utilization of a static gamma characteristic generally fails to provide adequate luminance for the LCD display because a static gamma characteristic cannot respond to changes in backlight brightness; low-quality rendered images thus ensues. While typical LCD displays can alter the gamma characteristic of a display on a frame-by-frame basis, such adjustment generally is insufficient for producing rich, compelling imagery.